1. Field of the Invention
The present invention relates to an electronic device and a wiring with a current induced cooling effect, such that internal elements of the electronic device can be directly cooled. The invention also relates to an electronic device capable of converting a temperature difference into a voltage.
2. Background Art
As a size of internal electronic elements used in integrated electronic devices (such as IC, LSI, and ULSI) becomes smaller and a level of their integration increases, the amount of heat generated inside the integrated devices increases. If the heat dissipation inside the devices increases over the operation limit, the devices may malfunction or might break down. it is therefore an important design issue how to cool the devices, especially to remove the heat generated inside the package to the outside. Until now, conventional cooling methods are used as the followings:                1. Use a material with high heat conductivity in the package of the devices;        2. Attach a heat-dissipating fin on the surface of the package;        3. Attach a heat-dissipating fin on the surface of the package, and blow on that fin by using an electronic fan; and        4. Install a water-cooled radiator or a Peltier cooling device attached on the surface of the package.Because these methods are the cooling from the outside of the package, it becomes inherently difficult to remove the heat generated inside integrated circuits to the outside as the sizes of electronic devices become smaller.        
Particularly in highly-integrated electronic devices, a multilayered structure is indispensable. In such structure the via-hole type wirings (interconnections) of sub-micron diameter are often used, which has a columnar shape connecting the layers by a conductor and are surrounded with an insulator. Since this wiring is fabricated perpendicularly to the plane of the layers and current flows along the structure, that shape is sometimes called as a CPP (current-perpendicular-to-plane) structure. As the size of a CPP structure wiring decreases, it is difficult to remove the Joule heating (resistive-heating by current) at the structure to the outside of the package.
When the current-resistance characteristics of a CPP structure wiring made of a single conducting material are measured, an increase in resistance that is proportional to the square of the current is observed. In the case of a CPP structure wiring made of a conventional metal (such as gold or copper) whose cross section is approximately 0.1 micrometers square, for example, an increase in resistance values corresponding to an increase of temperature of several to a dozen degrees is observed when a current of 1 mill-ampere flows. This phenomenon cannot be avoided no matter how the electronic device is cooled from the outside.
To remove the heat generated inside an electronic device to the outside efficiently, a semiconductor device that has a Peltier cooling device inside the package as the separate circuit has been proposed (Patent Document 1). In this method, however, the following problems arise:                1) Separate power is required for the cooling device;        2) Because the cooling circuit is separate from the main circuit to be cooled, the Peltier cooling part should be electrically isolated from the main circuit to be cooled. Therefore a large time constant should exist in dissipation of the heat, since the heat conductivity of the insulator is generally poor as compared with that of a conductor.        
There is also another problem of how to measure the local generation of heat inside an electronic device. The temperature of an electronic device has been measured using a temperature sensor such as a thermistor, a thermocouple, or by measuring the intensity of infrared radiation (a radiation thermometry). These methods, however, have the following problems:                1) Temperature can be measured only from the outside of the device; and        2) Positional resolution of temperature that can be achieved is no more than several micrometers.Positional resolution is limited by the size of the temperature sensor, or by the size of pixels (constituent elements) of a heat-analyzing device. Here, the heat-analyzing devices are an array of the photodiodes, photoconductive effect elements, CdS cells and so on, which are arranged in the matrix shape so as to provide the thermal-information in planar distribution. Those are the similar configuration of a CCD sensor in a digital camera. A Peltier effect in a CPP structure in micron size was reported (Non-patent Document 1); however, no method has been proposed whereby the temperature of an element inside an integrated circuit can be measured directly and locally.        
Patent Document 1: JP Patent Publication (Kokai) No. 08-274226 A (1996)
Non-patent Document 1: X. Fan, G. Zeng, C. LaBounty, E. Croke, C. C. Ahn, S. Huxtable, A. Majumdar, and A. Shakouri; “SiGeC/Si superlattice microcoolers,” Appl. Phys. Lett., vol. 78 (2001), pp. 1580.